In an inkjet recording method, an aqueous ink composition is jetted in a liquid droplet form onto a substrate from small holes based on electric signals which induce thermal or mechanical pulses. In response to the pulses, the ink is jetted in the form of liquid droplets, which are forced toward specific positions on a surface of the substrate. After once being applied to the surface, the liquid droplets are required to stay at the positions and maintain their dimensions to form an image with a proper resolution. Thereafter, the liquid droplets are dried and sufficiently fixed to the surface of the substrate.
With the recent innovative progress of the inkjet recording technique, the inkjet recording method is employed for higher-definition image recording (image printing) which used to be an application filed of photography and offset printing. Inkjet printers including a higher-viscosity ink head have been developed, which permit formation of clearer images with the use of a higher-viscosity ink. Hence, there is a demand for the higher-viscosity ink to be used with the higher-viscosity ink head.
An ink composition (PLT1) which contains an aqueous vehicle, a self-dispersive pigment, a silicone-containing surfactant and a polymer having a specific glass transition temperature (Tg), and an ink composition (PLT2) which contains at least a polymer, glycerin, a tackifier and water, for example, have been developed as aqueous inkjet ink compositions to be used for inkjet inks. In PLT2, a method of controlling the viscosity of the ink with the use of the tackifier is disclosed.